364 THE OCEAN. 
and Indian Oceans by two or three species nearly 
allied to it in structure, but furnished with a glassy 
shell. One of these is named Hyalea tridentata; 
Gass Sets. (Hyalea tridentata, and Cleodora pyramidata.) 
its shell is small and somewhat globular, resembling 
a bivalve without a hinge; the hinder part being 
consolidated and armed with three spines; the sides 
have a narrow fissure through which a semi-trans- 
parent membrane protrudes. The animal is fur- 
nished with a wing or fin on each side, which it uses 
as oars. A kindred species (Cleodora cuspidata) is 
of extreme delicacy and beauty. The shell is glassy 
and colourless, very fragile, nearly in the form of 
a triangular pyramid, with an aperture at its base, 
from which proceeds along and slender glassy spine; 
and a similar spine projects from each side of the 
middle of the shell. The animal is like the preced- 
ing; but the hinder part is globular and pellucid, 
and in the dark vividly luminous, presenting a sin- 
gularly-striking appearance, as it shines through its 
perfectly-transparent lantern. Both of these are 
found floating in great numbers on the surface of 
the sea. 
